The Use of Alternators on British Passenger Cars

Abstract

The need for generators of higher output ratings and improved performance at low engine speeds has resulted in the development and growing employment of alternators for battery charging systems on British passenger cars. This paper discusses some theoretical and practical problems in the specification, design and application of such alternators.

Part 1 covers the method of assessing the ‘Effective Output’ of an alternator by means of engine time-speed histograms, and shows the way in which this effective output is influenced by the drive ratio of the alternator. Empirical rules are put forward for deciding the effective output needed for a car with given electrical loading, and correlation is shown to exist between the empirical assessment and the results of practical vehicle running tests. The manner in which the alternator characteristics can be modified by the designer within a given overall size of machine, and the influence upon the effective output of such changes, are discussed.

Part 2 surveys the practical experience gained to date by the authors' company in the use of alternators on British passenger cars. The reasons leading to the present standard fixing arrangements for alternators arc described, together with suggested designs for the alternator mounting bracket which forms part of the engine. The different forms of noise emanating from an alternator are discussed.

The practical implications of achieving the desirable drive ratios lead to the conclusion that improved performance of the conventional belt drive arrangement will become necessary.

The paper concludes with some remarks on the philosophy of warning light indication, and describes some systems which meet the present requirements.